Currently, in the batch processing transformations selection we have an "add alpha" option, but there is no "remove alpha" option. It is possible to use the "convert > True colors" option, but this works only if the alpha channel is not messed up somehow. For instance, if the alpha channel were completely empty, then using the "True colors" conversion would also result in an empty image!!!

Another request would be a command to replace an arbitrary channel with a file, sort of the reverse of "Extract channel". This would be even more powerful!